Weather forecasters still rely on decades-old practice

Updated 6:13 pm, Sunday, May 13, 2018

LAS VEGAS (AP) — With all the technological advances in weather forecasting over the years, National Weather Service officials in Las Vegas and across the country still rely on a decades-old practice to fine tune their outlook — twice-daily launching of weather balloons.

A National Weather Service staff member, every day at 4 a.m. and 4 p.m., steps outside the office and launches a weather balloon, the Las Vegas Review-Journal reported .

The helium-filled latex balloon gradually rises more than 100,000 feet (30,480 meters) while towing instruments that measure temperature, humidity and air pressure.

The routine provides a vertical snapshot of the atmosphere that meteorologists can't get from weather instruments on the ground.

Meteorologists use the data to determine the "state of the atmosphere" and predict what will happen next across the continent and around the world.

Flights generally last about 90 minutes and end when the expanding balloon finally bursts from the internal pressure roughly 20 miles (32.2 kilometers) above the ground.

At launch, the biodegradable balloon is about 6 feet (1.8 meters) in diameter. By the time it pops, it's "about the size of a small house," said Chelsea Kryston, a meteorologist with the National Weather Service in Las Vegas.

"I've seen (the balloon explode) before," said John Adair, a senior forecaster for the weather service in Las Vegas. "All you see is a small, white speck, and then it just disappears."

It usually takes one of the packages 20 to 30 minutes to drift back down to the ground after its balloon pops roughly 20 miles above the ground.

Each package, known as a radiosonde, has its own bright orange parachute to slow it down during its long descent "so it doesn't knock anyone out," Kryston said.

The cardboard and foam package is a little smaller than a shoebox and comes printed with words "harmless weather instrument." It also comes with its own prepaid postage and packaging so anyone who finds one can mail it back.

Las Vegas is one of 93 sites around the country — and hundreds worldwide — that release weather balloons at the same time twice a day. When the clocks change for daylight saving time, so do the balloon launches, which shift to 3 a.m. and 3 p.m.

The releases happen regardless of the weather, though a powerful thunderstorm directly overhead might delay a launch by as much as 90 minutes, Kryston said.

Most weather service offices fill their balloons with hydrogen, which is cheaper than helium but also flammable, Kryston said, requiring a special shelter and other safety features the Las Vegas office does not have.